JP4321573B2 - Lithographic ink printing method - Google Patents

Description

  The present invention is a lithographic printing method comprising four process colors of yellow, red, indigo and black, which is superior in reproducible color rendering area (gamut) than the ISO standard Japan color ink, and further increases the density. The present invention relates to a printing method capable of reproducing a wider color rendering area.

  The IT revolution that began in the 1990s has led the environment surrounding the printing site to the direction of digitalization, and this digitalization has allowed the workflow of conventional printing methods (photographing, positive, scanning, data, design, EPS).・ Imposition, film, printing plate, printing) was a multi-stage process, but we succeeded in dramatically shortening the process with digital camera shooting, DTP, CTP, and printing. As a result, “RGB” conversion of the submitted data is being standardized, and the current situation is that the data to be handled is shifting to a wider color reproduction region.

  However, in lithographic offset printing consisting of four process colors (CMYK) of yellow, red, indigo and black, which are currently mainstream, the data submitted as “RGB” is separated into CMYK in a narrower color reproduction area. Inevitably, there is a problem that color reproduction is not successful unless the color space is set at the photographing stage or the final color conversion from “RGB” to “CMYK” is performed appropriately. In such an environment, “standardization” is an important point, and “Japan Color” is also attracting attention as one means of standardization.

  On the other hand, in lithographic offset printing consisting of the four colors of yellow, red, indigo, and black, the hue is due to subtractive color mixing, so the hue becomes cloudy each time the colors are overlapped, and the color reproduction area is inevitably higher than that of RGB. However, the difference in color reproducibility between digital data and printed matter became a problem. Although it was possible to enlarge the color reproduction area somewhat by increasing the printing density of each ink, the color rendering area that can reproduce the turbidity of the hue, which is the limit of subtractive color mixing, was narrowed.

As means for solving this, in Patent Document 1, a printing method using an ink set of 5 to 7 colors is established as a high-saturation printing system. As a printing method using an ink set having each specified hue, process 4 colors are used. 6 colors (hexachrome printing) with orange and green added to 7 colors and 7 colors (high fidelity printing) with orange, green and purple added to 4 process colors have been established. In addition, as represented by hexachrome ink, there are also methods such as adding fluorescent pigments to some colors as a means of suppressing the turbidity of not only primary colors but also secondary and tertiary colors and expanding the color reproduction range. However, there are also disadvantages such as deterioration of printability (transfer defects, gloss reduction, etc.) and fading of printed matter due to insufficient light resistance. Furthermore, the number of ink colors used is 6 or 7, and an expensive multicolor printing machine with 6 or more printing cylinders is required. It is an indispensable condition, and it is limited to using this system due to huge capital investment and complicated color management to start a new one.
JP 2001-260516 A

  The present invention has been made in order to solve such problems in the prior art, and the problem is that a Japanese color of ISO standard is used by using a four-color printing machine that has been widely used in the past. A lithographic ink consisting of four process colors of yellow, red, indigo and black, which is superior in reproducible color rendering area (gamut) than compliant inks. By increasing the printing density, a wider color rendering area can be reproduced. It is to provide a printing method.

In general, in order to expand the color reproduction region, it is necessary to approximate the ideal spectral reflectance curve of each color.
That is, the wavelength range in which a person recognizes color is 400 nm to 700 nm light (this wavelength is referred to as visible light). In yellow ink, the reflectance in the wavelength range of 500 nm to 700 nm is 100%, and the wavelength range of 400 nm to 500 nm. The red ink has a reflectance of 0%, and the red ink has a reflectance of 100% in the wavelength region of 400 nm to 500 nm and 600 nm to 700 nm, and a reflectance of 0% in the wavelength region of 500 nm to 600 nm. Therefore, it is said that it is ideal that the reflectance in the wavelength region of 400 nm to 600 nm is 100% and the reflectance in the wavelength region of 600 nm to 700 nm is 0% (the spectral reflectance of the ideal process ink) Curves are shown in Table 6).

However, the reflection spectrum of the ink composition for offset printing of yellow, red, indigo and black, which is currently used in four process colors, is far from the ideal reflection spectrum. Since there is unnecessary absorption in the part that must be completely reflected, a turbid component of the ink exists, and the color reproducibility is narrowed.
That is, according to the present invention, in lithographic printing using any two or three of yellow ink, red ink and indigo ink, and black ink, each density value of yellow, red and indigo is set to 1. L * when each color ink is printed individually and in layers within the range of 40 to 1.44, red is 1.52 to 1.56, and indigo is 1.63 to 1.67 (reference density value). a * b * color system (JIS Z
8729), the horizontal axis a * is sliced in increments of −120 to +120, the vertical axis b * is incremented by 10 steps in the range of −120 to +120, and the height L * is divided into increments of 10 steps of 0 to 100. Using each color ink whose number of expressible colors defined by the color reproduction area expressed as above is 1.1 times or more of ISO standard Japan color compliant ink, the density is 1.0 to 1.5 of the standard density value. The present invention relates to a lithographic printing method characterized by printing as double.

Furthermore, in the present invention, each L * a * b * value of the reference density value is
Yellow ink, L *: 87 to 95, a *: -4 to -12, b *: 90 to 100
Red ink, L *: 50 to 55, a *: 75 to 83, b *: -14 to -20
Indigo ink, L *: 52 to 58, a *: −40 to −45, b *: −45 to −53
The L * a * b * values of the above two ink overprints are L *: 51 to 56, a *: 65 to 70, b. *: 56-61, indigo ink x yellow ink, L *: 47-53, a *: -77 to -83, b *: 25-32, indigo ink x
By red ink printing, L *: 23 to 29, a *: 28 to 33, b *: −63 to −68
The present invention relates to the above printing method, characterized in that an ink that falls within the range is used.
Furthermore, these (a) yellow, (b) red, and (c) indigo relate to the above printing method having the following reflectance.
(A) In the wavelength region of 400 nm to 700 nm, when the maximum reflectance is 100%, the wavelength region of 400 nm to 480 nm is 1 to 20%, and the reflectance in the wavelength region of 530 nm to 700 nm is 90 to 100%. A yellow ink containing 5 to 15% by weight of a yellow phase compound having a reflection spectrum with respect to the total weight of the ink.

(B) In the wavelength region of 400 nm to 700 nm, when the maximum reflectance is 100%, the maximum reflectance in the wavelength region of 400 nm to 500 nm is 50% to 100%, and the reflectance in the wavelength region of 500 nm to 560 nm. A red ink containing 15 to 30% by weight of a red hue compound having a reflection spectrum of 1 to 20%, a reflectance of 630 nm to 700 nm and a reflectance spectrum of 90% to 100% based on the total weight of the ink.
(C) In the wavelength region of 400 nm to 700 nm, when the maximum reflectance is 100%, the reflectance in the wavelength region of 400 nm to 530 nm is 50 to 100%, and the reflectance of 600 nm to 700 nm is 1 to 30%. An indigo ink containing 10 to 25% by weight of an indigo hue compound having a spectrum with respect to the total weight of the ink.

  By using the lithographic ink printing method provided by the present invention, in addition to the conventional four colors of yellow, red, indigo, and black ink, it was expressed by six colors or seven colors printing that added orange, green, purple, etc. The RGB color reproduction region can be reproduced with four colors of yellow, red, indigo, and black. Furthermore, by increasing the density of the printed matter, it is possible to reproduce a wider color reproduction region than the conventional process four-color ink. Further, in the present invention, since a fluorescent pigment is not used as a means for improving the color reproduction region of the printed material, it is possible to obtain a printed material with high saturation without degrading the printability and the fading of the printed material over time.

  Next, the present invention will be described more specifically with reference to preferred embodiments.

  The present invention comprises a pigment, a vehicle component obtained by heating and dissolving a synthetic resin, a vegetable oil, and a petroleum solvent together with a gelling agent such as aluminum stearate or aluminum chelate as necessary, and an auxiliary agent such as a friction-resistant agent. It is a lithographic ink consisting of four colors: yellow, red, indigo and black.

  In the present invention, the “density value” refers to ISO standard Japan color standard paper, for example, “Tokuhishi Art Double Sided Plates / 110 kg” manufactured by Mitsubishi Paper Industries Co., Ltd. The density value when measured with a Macbeth D196 densitometer.

As a method for expressing the color reproduction area, an XYZ color system (CIE 1931 color system), an X ₁₀ Y ₁₀ Z ₁₀ color system (CIE 1964 color system), an L * a * b * color system (CIE 1976), Hunter Lab color system, Munsell color system, L * u * v * color system (CIE1976), and the like. In the L * a * b * color system, “brightness” is expressed by L * as the degree of brightness that can be compared regardless of hue, and indicates that the color becomes brighter as L * increases and becomes darker as it decreases. . In addition, “hue” that differs depending on each color is indicated by a * and b * values, a * indicates a red (+) to green (−) direction, and b * indicates a yellow (+) to blue (−) direction, In each direction, the color becomes brighter as the absolute value increases, and the color becomes dull as it approaches 0. This makes it possible to digitize one color using L *, a *, and b *.
In addition to “lightness” and “hue”, there is “saturation (C)” as a method for digitizing the degree of vividness, which can be obtained by the following calculation formula.

Similarly, C shows that the color becomes brighter as the absolute value increases, and the color becomes dull as the value decreases.
All color reproduction areas that can be represented by a single printed matter (including color spaces other than printed matter) are called color rendering regions (gamut). The simplest way to represent gamut is as follows: a * is the horizontal axis, b * vertical axis In the two-dimensional space, single color solid part (yellow, red, indigo) and single color solid print overprint part (yellow ×
(Red, red x indigo, indigo x yellow) It is possible to express the a * vs. b * values of a total of six colors as a plotted hexagonal area. The larger the gamut area, the wider the color reproduction area.
In the present invention, the color space (color space) in the L * a * b * color system is represented by the horizontal axis a * as a color rendering region considering not only the two dimensions of a * and b * but also the lightness “L *”. Is expressed in 10-step increments in the range of -120 to +120, and the height L * is expressed by slicing in 10-step increments from 0 to 100. The color reproduction area indicating the number of colors is schematically expressed, and the larger the number of reproduced colors, the larger the color rendering area that can reproduce the ink.

Japan Color is a standard color for printing established by the ISO / TC130 National Committee. In offset sheetfed Japan Color 2001, colorimetric values (L * a * b) of ISO12642 patterns (928 colors, also referred to as IT8) * Value) is shown as data. Based on the standard conditions of international standard ISO12647-2 for commercial offset printing, the printing conditions are the inks and printing papers that are normally used in Japan (Japan Color 2001 determines four types of paper). Defined by use. L * of yellow, red, indigo and single color solid parts when printing on general Japan color ink on Japan color standard paper, for example, "Special Rhibo Art Double Sided Plate / 110kg" manufactured by Mitsubishi Paper Industries Co., Ltd. The a * b * value and the calculated C value are yellow ink, L *: 86, a *: -7, b *: 92, C: 92, red ink, L *: 45, a * : 72, b *: -5, C: 72, indigo ink, L *: 54, a *: -36, b *: -49, C: about 61.

The ink of the present invention has a density range of 1.40 to 1.44 for yellow, 1.52 to 1.56 for red, and 1.63 to 1.67 for indigo (hereinafter referred to as “reference density value”). ), The chromaticity according to the L * a * b * color system of the single color and the overprint of each single color, and the C value are yellow ink, L *: 87 to 95,
Preferably 88 to 93, a *: −4 to −12, preferably −5 to −10, b *: 90 to 10
0, preferably 92 to 98, C: 92 to 99, red ink, L *: 50 to 55, preferably 51 to 54, a *: 75 to 83, preferably 76 to 81, b *: -14 to −20, preferably −15 to −18, C: 77 to 83, indigo ink, L *: 52 to 58, preferably 52 to 57, a *: −40 to −45, preferably −41 to −44 , B *: −45 to −53, preferably −46 to −51, C: 62 to 67, and further, red ink × yellow ink, L *: 51 to 56, a *: 65 to 70 , B *: 56 to 61, C: 86 to 93, indigo ink x yellow ink, L *: 47 to 53, a *: -77 to -83, b *: 25 to 32, C: 81 ~ 87, indigo ink x red ink, L *: 23 to 29, a *: 28 to 33, b *: -63 to -68, C: 69 to 75 Boasting.
That is, the combination of the inks of the present invention has a C value larger than that of Japan color compliant inks, and boasts high color reproducibility.
Furthermore, as a feature of the present invention, when the density is increased to about 1.0 to 1.5 times, the color reproducibility is higher than that of the conventional ink. Specifically, when it is increased to 1.45 times the reference density value, it has a high reproducibility of 1.5 times or more of the number that can be expressed by the reference density value.

In addition, one of the major features of the present invention is that the number of reproducible colors in the “B (blue violet)” region of RGB, which has been difficult to reproduce with conventional inks, increases. That is, L *
The color space in the a * b * color system is represented by 10 steps each having a horizontal axis a * of −120 to +120 and a vertical axis b * of −120 to +120, and a height L * of 0 to 100. In the color reproduction region expressed by slicing each segment, the number of expressible colors in the range of L *: 10 to 40, a *: 40 to 60, b *: -40 to -70 is larger than that of the conventional ink. .

The yellow pigment used in the present invention is a disazo yellow compound such as CI Pigment Yellow 12, CI Pigment Yellow 13, and the like on a black ink printed within a density value range of 1.85 to 1.90. In addition, if the density of the yellow ink was overprinted in the range of 1.40 to 2.10, and the L * value had transparency not exceeding 17, overprinting of secondary and tertiary colors was performed. It is possible to obtain a good color reproduction region with little influence on the underprint ink. Further, CI Pigment Yellow 83 can be used as a complementary color by adding 0.5 to 10% by weight, preferably 2 to 5% by weight, based on the total weight of the yellow pigment.

  Examples of red pigments include, but are not limited to, rhodamine-based dyes such as rhodamine B, rhodamine 3G, rhodamine 6G, molybdenum, tungsten metal lake compounds such as C.I. Pigment Red 81 and C.I. Pigment Violet 1.

  Examples of indigo pigments include phthalocyanine compounds such as C.I. Pigment Blue 15: 3 and C.I. Pigment Blue 15: 4. Furthermore, C.I. Pigment Green 7 may be used as a complementary color by adding 5 to 15% by weight, preferably 8 to 11% by weight, based on the total weight of the indigo pigment.

The copper phthalocyanine compound, which is a cyan pigment used in the present invention, is a substance exhibiting a crystal polymorphism (homogeneous heterocrystal), and α, β, γ, ε, π, τ, ρ, χ depending on the crystal structure. However, it is preferable to use a β-type having excellent crystal stability and dispersibility, and further a fine β-type copper phthalocyanine having a specific surface area of 74 m ² / g or more. preferable.

  Examples of the black pigment include carbon black such as C.I. Pigment Black 7.

As the synthetic resin used in the present invention, rosin-modified phenol resin, petroleum resin, alkyd resin, rosin-modified alkyd resin, petroleum resin-modified alkyd resin, rosin ester and the like can be considered. Preferably, a rosin modified phenolic resin is used. The rosin-modified phenol resin is not particularly limited, but it is preferable to use a resin having a weight average molecular weight of 10,000 to 300,000. When the molecular weight is 10,000 or less, the viscoelasticity of the ink is lowered, and when it is 400,000 or more, the fluidity as the ink becomes insufficient.

Examples of vegetable oils include those derived from vegetable oils such as palm kernel oil, palm oil, cottonseed oil, peanut oil, palm oil, corn oil, olive oil, linseed oil, corn oil, soybean oil, safflower oil, and tung oil, Those thermal polymerized oils and oxygen-blown polymerized oils can also be used. Moreover, in this invention, these vegetable oils may be used independently and can also be used in combination of 2 or more type.

The petroleum solvent used in the ink has an aromatic hydrocarbon content of 1% or less, an aniline point of 75 to 95 ° C, preferably 80 to 95 ° C, and a boiling point of 260 to 350 ° C, preferably 280 to 350. It is a petroleum solvent in the range of ° C. If the aniline point is less than 75%, the ability to dissolve the resin is too high, which is not preferable because the ink setting property is slow, and if it exceeds 95 ° C., the resin solubility is poor, so Meat etc. are bad and not preferable. When the boiling point is less than 260 ° C., the evaporation of the ink solvent on the printing machine increases, and the transferability of the ink to a roller, a blanket, a plate, or the like deteriorates due to the deterioration of the fluidity of the ink. Moreover, when it exceeds 350 degreeC, since drying of heat set type ink is inferior, it is not preferable.

Further, the lithographic ink composition of the present invention includes a gelling agent, a pigment dispersant, a metal dryer, a drying inhibitor, an antioxidant, an anti-friction agent, an anti-set-off agent, and a nonionic surfactant as required. Additives such as agents and polyhydric alcohols can be used as appropriate.

[Example]
EXAMPLES Next, although an Example demonstrates this invention further in detail, the scope of the present invention is not limited to these description Example. In addition, the part of the following description represents a weight part and% represents weight%.

Example of production of rosin-modified phenolic resin To a four-necked flask equipped with a stirrer, a cooler, and a thermometer, 1000 parts of P-octylphenol, 850 parts of 35% formalin, 60 parts of 93% sodium hydroxide, 1000 parts of toluene, The reaction was carried out at 90 ° C. for 6 hours. Then, 125 parts of 6N hydrochloric acid and 1000 parts of tap water were added, stirred and allowed to stand, and the upper layer part was taken out to obtain 2000 parts of a toluene solution of a resole type phenol resin having a nonvolatile content of 49%. It was.
A four-necked flask equipped with a stirrer, a condenser with a water separator, and a thermometer was charged with 1000 parts of gum rosin, dissolved at 200 ° C. while blowing nitrogen gas, and 1800 parts of the resole solution produced above was added. After reacting at 230 ° C. for 4 hours while removing toluene, 110 parts of glycerin was added, and reacted at 260 ° C. for 10 hours, with an acid value of 20 or less, a weight average molecular weight of 50000, Shin Nippon Petrochemical Co., Ltd. AF Solvent 6 A rosin-modified phenol resin having a cloudiness temperature of 90 ° C. was obtained.

Example of varnish production 40 parts of rosin-modified phenolic resin, 15 parts of tung oil, 30 parts of soybean oil, 14 parts of AF Solvent No. 6 (solvent manufactured by Shin Nippon Petrochemical Co., Ltd.), ALCH (gelator manufactured by Kawaken Fine Chemical Co., Ltd.) 1.0 part was heated and stirred at 190 ° C. for 1 hour to obtain a varnish.

Ink Example 1 (yellow ink)
In the formulation shown in Table 1, C.I. I. Pigment Yellow 12 (LIONOL YELLOW 1235-P manufactured by Toyo Ink Manufacturing Co., Ltd.) was subjected to primary dehydration by gradually adding varnish and kneading in a kneader at a temperature of 75 ° C. Next, vacuum dehydration was performed for 1 hour under conditions of a kneader temperature of 100 ° C. to 120 ° C. and a degree of vacuum of 76 mmHg, and secondary dehydration was performed so that the water content in the base ink was 0.5% or less. After dehydration, the remaining varnish and petroleum solvent were added, kneaded and diluted, and the undispersed base ink was taken out from the kneader. The extracted base ink was kneaded using a three roll with a roll temperature of 60 ° C. with a dispersed particle measuring machine (grind meter) to 7.5 μm or less to obtain yellow base ink 1. Subsequently, varnish, soybean oil, a compound, a metal dryer, and a drying inhibitor were added to the base ink 1 according to the formulation shown in Table 2 to obtain a yellow ink 1.

Ink Example 2 (Red ink)
As with the yellow ink, C.I. I. A red base ink 2 was obtained using Pigment Red 81 (Funal Rose RNN-P manufactured by Fuji Kasei Co., Ltd.). Next, soybean oil 2, a compound, a metal dryer, and a drying inhibitor were added to the base ink 2 in the formulation shown in Table 2 to obtain a red ink 2.

Ink Example 3 (Indigo Ink)
In the formulation of Table 2, C.I. I. Pigment Blue 15: 3 (LIONOL BLUE GLA-SD manufactured by Toyo Ink Manufacturing Co., Ltd.), C.I. I. Pigment Green 7 (LIONOL GREEN YS-2A manufactured by Toyo Ink Mfg. Co., Ltd.) is mixed with varnish, mixed with a dispersed particle measuring machine (grind meter) until 7.5 microns or less, and then soybean oil and compound Then, a metal drier and a drying inhibitor were added to obtain indigo ink 3.

In addition, the ink used as a comparative example can be any oxidative polymerization type lithographic printing ink compliant with Japan Color. Here, TK high unity colors were used.

Printing Evaluation Test For the inks of the above examples and comparative examples, an ISO12642 chart (IT8 chart) is put on the printed matter, and the yellow, red, and indigo solid density values are set to yellow: 1.40 to 1 under the following printing conditions. .44, red: 1.52-1.56, indigo: 1.63-1.67, and the printed matter was evaluated. The black ink was printed using a general oxidation polymerization type lithographic printing ink within a density value range of 1.88 to 1.92.

Printing conditions Printing machine: Heidelberg Speedmaster Kikuzen 4-color machine (Heidelberg Japan Ltd.)
Paper: Tokishi Art Double Side 110Kg (Mitsubishi Paper Co., Ltd.)
Dampening solution: Astro Mark 3 (Niken Chemical Laboratory Inc.) 2.0% tap aqueous solution Printing speed: 10,000 sheets / hour Concentration: Monochrome (yellow, red, indigo, ink) of printed matter at D196 manufactured by Gretag Macbeth ) Measure the density value of the solid part.

Colorimetry: Monochrome solid part (yellow, red, indigo) and monochromatic solid overprint part (yellow x red, red x indigo, indigo x) with SpectroEye (D50, 2 degree field of view, StatusT) manufactured by Gretag Macbeth Yellow) L *, a *, b * values are measured.
The C value was determined from the following formula using a * and b *.

The results are shown in Table 3. Compared to the comparative example, the C value of the example is large, and the chroma of the printed matter is high.

Printed matter measurement conditions Create an ICC profile from the measurement results of the ISO12642 chart.
Using the created ICC profile, Adobe Photoshop is used to convert the image to an L * a * b * image. The color space (color space) in the L * a * b * color system is represented by the horizontal axis a *.
A color reproduction region (120 to +120, the vertical axis b * is expressed by 10 step intervals within the range of −120 to +120, and the height L * is expressed by being sliced by 10 step intervals from 0 to 100 ( The maximum number of colors was 6875 (Table 4). The colored part in the figure indicates a reproducible color, and the gray part indicates a color that cannot be reproduced.

Further, Table 7 shows the obtained spectral reflectance curve. Compared to the conventional ink of the comparative example, the ink of the example is closer to the ideal spectral reflectance curve, and unnecessary absorption of the portion that must be completely reflected is reduced. For this reason, the turbidity component of the ink is reduced and the color reproduction region is widened (Table 4).

Furthermore, Table 5 shows the results of performing the same printed matter evaluation after printing with the printed matter density increased to 1.45 times the reference density under the same printing conditions.

Using this expression method, yellow, red, and indigo density values are set on ISO standard Japan color standard paper, for example, “Tokuhishi Art Double Sided Plates / 110 kg” manufactured by Mitsubishi Paper Industries Co., Ltd. When printing within the range of 40 to 1.44, red 1.52 to 1.56, and indigo 1.63 to 1.67, only 741 colors can be reproduced with general ISO standard Japan color compliant ink. In contrast, the ink of the present invention can reproduce approximately 1.17 times 871 colors, and when the density is increased to 1.45 times the above range, the Japan color compliant ink is 1050 colors. On the other hand, with the ink of the present invention, it is possible to reproduce up to 1323 colors (1.26 times the Japan color compliant ink ratio), which is about 1.52 times the reference density value.

  Therefore, in the present invention, a printing method capable of expressing a wider color rendering region by using a printing method in which the ink itself has a color reproduction region that could not be reproduced by conventional inks and further increases the density. I found.

Claims (1)

In lithographic printing using any two or three of yellow ink, red ink and indigo ink, and black ink, each density value of yellow, red and indigo is set to 1.40 to 1.44 for yellow. L * a * b * color specification when each color ink is printed individually and superimposed within the range of 1.52 to 1.56 for red and 1.63 to 1.67 for indigo (reference density value) The color space in the system (JIS Z 8729) is expressed in steps of 10 in the range of −120 to +120 on the horizontal axis a *, −120 to +120 on the vertical axis b *, and 10 steps of height L * from 0 to 100. Using each color ink whose number of expressible colors defined by the color reproduction area expressed by slicing at a break of 1.1 is 1.1 times or more the ISO standard Japan color compliant ink, the density is set to 1.0 as the reference density value. A lithographic printing method for printing as 1.5 times,
Among the color inks, yellow ink is C.I. I. Pigment yellow 12 or C.I. I. When the pigment yellow 13 is used and the density of the yellow ink is overprinted in the range of 1.40 to 2.10 on the black ink printed within the range of the density value of 1.85 to 1.90, the L * value is The ink does not exceed 17.
Red ink is C.I. I. Pigment red 81 or C.I. I. It is an ink using Pigment Violet 1,
Indigo ink is a C-type copper phthalocyanine compound having a specific surface area of 74 m ² / g or more as an indigo pigment. I. Pigment blue 15: 3 or C.I. I. It is an ink using Pigment Blue 15: 4,
Black ink is a pigment that contains C.I. I. An ink using CI Pigment Black 7,
Each color ink Ri Oh in ink capable of high-density printing,
And each L * a * b * value of the reference density value is
Yellow ink, L *: 87 to 95, a *: -4 to -12, b *: 90 to 100
Red ink, L *: 50 to 55, a *: 75 to 83, b *: -14 to -20
Indigo ink, L *: 52 to 58, a *: −40 to −45, b *: −45 to −53
The L * a * b * values of the above two ink overprints are in the range of
Red * yellow ink, L *: 51-56, a *: 65-70, b *: 56-61
L *: 47-53, a *: -77 to -83, b *: 25-32
L *: 23 to 29, a *: 28 to 33, b *: −63 to −68
A lithographic printing method characterized by using an ink that falls within the range .